Immunological adjuvants are substances that, incorporated to the antigen (Ag) or simultaneously administered with it, induce a more effective immune response against the antigen. They may be used to enhance the immune response against an Ag in several ways: they can enhance the magnitude of the immune response against a weak Ag; increase the rate and duration of the immune response, modulate antibody (Ab) avidity; isotypes or subclass distribution; stimulate and modulate the cellular immune response; promote the induction of local immune response (e.g., mucosa); decrease the amount of necessary Ag and reduce the vaccine cost; or they may help in avoiding Ag competence which exists in combined vaccines (Singh and O'Hagan. Advances in vaccine adjuvants. Nat Biotechnol. 17 (11):1075-81. 1999).
Throughout vaccine history, and ever since the complete Freund adjuvant (CFA) based on a mycobacterial emulsion with water and oil, many preparations have been tested with higher or lower success. The most used and allowed adjuvant for human use is aluminum, as hydroxide or phosphate salts. Other adjuvants consist of bacterial components such as endotoxins, particles such as liposomes, oil emulsions such as saponins, and other different molecules (Petrovsky and Aguilar. Vaccine adjuvants: current state and future trends. Immunol Cell Biol. 82 (5):488-96. 2004). Most of the historically used adjuvants, such as aluminum salts, preferably stimulate the T helper (Th) type 2 immune response (Liljeqvist and Stahl. Production of recombinant subunit vaccines: protein immunogens, live delivery systems and nucleic acid vaccines. J Biotechnol. 73 (1):1-33. 1999), increasing the production of Abs. However, there are other vaccines, such as BCG vaccine and adjuvants incorporating oil compounds, which stimulate the Th1 immune response (Victoratos, Yiangou, Avramidis and Hadjipetrou. Regulation of cytokine gene expression by adjuvants in vivo. Clin Exp Immunol. 109 (3):569-78. 1997). The choice of the adjuvant for a vaccine should be carefully selected in the future, not just as a function of the amount of response, but also on the quality of the elicited response. On the other hand, the traditionally used vaccination methodology (intramuscular or intradermic vaccine in aluminum hydroxide) has been useful for inducing systemic humoral immune responses but generally fail to induce cellular and local immune responses, such as in mucosa (Moyle, McGeary, Blanchfield and Toth. Mucosal immunization: adjuvants and delivery systems. Curr Drug Deliv. 1 (4):385-96. 2004). There is a greater need in the design of vaccines capable of inducing strong cellular Th1 type and cytotoxic T cell (TCL) immune responses which may prevent viral chronic infections, infections related to intracellular pathogens or cancer (therapeutical vaccines) (Seder and Hill. Vaccines against intracellular infections requiring cellular immunity. Nature. 406 6797):793-8. 2000).
Other important considerations, (besides promoting a specific and efficient immune response against the antigen) are related to those important features for the substance to be used in clinical practice. Optimal formulations must be safe, stable, biodegradable, inert and of low manufacturing cost. The list of substances complying with all these requirements is quite short, up to now, the adjuvants approved for use in humans are restricted to aluminum salts, MF59 (an oil in water emulsion), MLP (monophosphoryl-glycolipid), viral particles (HBV and HPV), IRIV (proteoliposome composed of phospholipids, influenza virus hemagglutinin and a determined target antigen); and the B subunit of the cholera toxin (Reed, Bertholet, Coler and Friede. New horizons in adjuvants for vaccine development. Trends Immunol. 30 (1):23-32. 2009). Adjuvants must not induce adverse reactions when used in prophylactic vaccines, although certain reactions are accepted in therapeutic vaccines. In the veterinary health field, efficacy is an element of great importance and certain levels of side effects are tolerated (Sesardic. Regulatory considerations on new adjuvants and delivery systems. Vaccine. 24 Suppl 2 S2-86-7. 2006).
Given that the main entry for the majority of infections are mucosal surfaces, the ability to generate mucosal immunity after administration of an Ag could provide for an early defense against these pathogens. Unfortunately, after administration of Ags by the oral route, there is degradation in the gastrointestinal tract, little absorption and low long-term efficacy, therefore repeated administrations and large amounts of Ag are needed for stimulating and maintaining the immune response. In addition, it has been observed immunological tolerance to those soluble Ags administered through the oral route (Moyle et al. Mucosal immunization: adjuvants and delivery systems. Curr Drug Deliv. 1 (4):385-96. 2004). Oral adjuvants used up to now, such as cholera toxin (TC), for instance, show serious risks after administration (Fujihashi, Koga, van Ginkel, Hagiwara and McGhee. A dilemma for mucosal vaccination: efficacy versus toxicity using enterotoxin-based adjuvants. Vaccine. 20 (19-20):2431-8. 2002), hence it is very important in this field to develop safer adjuvants that allow an efficient delivery of the Ags to the mucosal surfaces, with subsequent induction of immune response in the mucosa.
At the international level, the list of products with adjuvant properties is continuously larger; however, only a reduced number is used in the formulation of veterinary and human vaccines (Aucouturier, Dupuis and Ganne. Adjuvants designed for veterinary and human vaccines. Vaccine. 19 (17-19):2666-72. 2001; Petrovsky et al. Vaccine adjuvants: current state and future trends. Immunol Cell Biol. 82 (5):488-96. 2004). For that reason, it is important to develop efficient adjuvants that, at the same time, are safe for human and animal vaccines.
Nowadays, the majority of adjuvants capable of inducing strong Th1 responses are those based on oil emulsions, such as the incomplete Freund adjuvant (IFA), however, these entail adverse reactions at the site of injection, such as sterile abscesses and granulomas. In light of the foregoing, the development of parenteral and mucosal adjuvants which induce Th1 and CTL responses is highly relevant.
In the present invention, two new adjuvants are provided: Omp16S and Omp19S. These substances increase and/or modulate immune responses against co-administered Ags, favoring the development of Th1-, Th17- or CTL-type immune responses.